In the case of high power gear installations, particularly those intended for high speed operation, forced or pressure lubricated of the bearings and the toothed wheels is essential. To achieve this, at least one lubricating oil pump is provided in each such installation. This pump is either driven mechanically by the gear installation itself or, for example, by a separate electric motor. Since, in most cases, a fairly large amount of heat is transferred to the lubricating oil, the oil is usually cooled down in a separate oil cooler after emerging from the pump. In the known gear installations, the oil is retained in an oil reservoir which, together with the oil pump and the oil cooler, is housed in a special oil unit which is quite separate from the gear housing.
This conventional arrangement leads to a number of disadvantages where pressure lubrication is required, as will now be discussed.
Prior to start-up and during the acceleration or run-up period lubrication is necessary to preserve a gear from damage. This is particularly important in the case of gears which form part of emergency devices or mechanisms and therefore run only very rarely. During the long periods of disuse the bearings dry out, so that these gears are likely to be considerably damaged if they are started-up without prior lubrication. To provide prior lubrication an electrically-driven pump can be provided, since a pump driven mechanically by the gear itself would not, at that time, be operational. However, as this electrically-driven pump is used only for the start-up, and is not used during normal operation of the gear, it represents an unacceptable additional construction expense.
Gear lubrication points also have to be supplied with sufficient oil during the run-down period of a gear, which run-down or slowing period may be of considerable length. In the case of gears having mechanically positively-driven pumps, supplementary pumps driven by electric motors have to be switched on to provide lubrication during the run-down period as the delivery of the positively-driven pumps fails as soon as the speed drops.
In the case of gears having main pumps driven by electric motors, these pumps have to remain switched on during the run-down period. However, it is important to note that in the case of all known gear installations having pressure lubrication, any damage to the pump or failure of the electrically supply will leave the installation without an oil supply and therefore susceptible to damage.
An object of the present invention is to provide a compact gear installation whereby dry-running upon start-up and run-down of the gear as well as upon failure of the oil-pump may be avoided.